The present invention relates to pressure-emitting assemblies for hydraulic brake circuits, used in motor vehicles, and more particularly to those which consist of a double, also called tandem, booster and a master cyclinder.
Assemblies of this type are well-known in brake engineering. In a conventional manner, the double booster comprises, in an outer casing, a fixed partition defining, inside this casing, a front space and a rear space, each space being divided in a sealed manner into a front chamber and a rear chamber by a movable partition, at least one elastic means tending to displace a movable partition rearward, at least one passage connecting the two front chambers and at least one passage connecting the two rear chambers, a pressure difference being established between the front and rear chambers of the rear space by a valve means on actuation of a control rod in order to actuate an output rod. This output rod actuates in turn the piston of a master cylinder, which produces a rise in pressure in at least one hydraulic brake circuit.
Assemblies of this type are arranged in a conventional manner in the engine compartment of the vehicle, where the space available is becoming less and less as manufacturers attempt to arrange an increasing number of accessories while observing the streamlining of the engine hood.
Manufacturers therefore tend to try and incorporate different systems into one, while observing the safety standards of course.
In addition, there are various situations where it is desirable to create an increase in pressure in the brake circuit without the control of the driver of the vehicle, such as, for example, to prevent the wheels from spinning on starting, to act as an antitheft device, and for hill starts, etc...
The known systems for the prevention of spinning on starting comprise driving-wheel speed sensors connected to a computer. When the computer detects a tendency of the wheels to spin, a known technique consists in controlling the braking of the driving wheels as in FR-A-2,513,201. This solution leads to extremely complex, fragile, bulky and expensive embodiments. Moreover, during the periods of antispin operation, the actuation of the brakes causes the brake pedal to be depressed, which may surprise the driver since, if he wishes to brake during these periods, his foot will not find the brake pedal in its usual place.
The known antitheft systems act on various control or operating members of the vehicle, and are always elements which are added to the engine compartment. Some of them actuate the brakes if the vehicle is occupied by an unauthorized driver, and are again complex, bulky and expensive systems.
By way of an aid to driving, manufacturers have also developed systems providing assistance with hill starts. These systems keep the brakes applied until the accelerator pedal is actuated. These systems are a further addition to the above and have the same disadvantages.